The present invention relates to a method for imaging non-linear parameters of tissues of an organ and an ultrasonic diagnostic apparatus using the method.
In a prior art ultrasonic diagnostic apparatus, an ultrasonic wave having a given frequency is transmitted into an organ, and a reflected wave from the inside the organ is detected, so that the distribution of the intensity of the reflected wave is imaged as an ultrasonic tomographic image (B-mode image) used for diagnosis. Since the diagnosing apparatus derives an image from a linear parameter, i.e., the intensity of the reflected wave (reflection coefficient), the obtained tomographic image does not directly represent structural characteristics of the tissues of organs, in other words, the acoustic characteristics of the tissues of organs.
Recently, there are extensive requirements for detecting the structural characteristics of the tissues of organs using ultrasonic waves for the purpose of diagnosis. The structural characteristics of organs include attenuation of the ultrasonic wave, speed of propagation thereof, diffusion, and non-linear parameters (coefficients). From among them, according to the non-linear parameter indications, characteristics of the tissues of organs can be easily detected.
An attempt to image non-linear parameters of an organ is disclosed in "Real-Time Non-linear Parameter Tomography" by Nobuyuki Ichida et al, Review of the 43-rd meeting of the Japan Society of Ultrasonics in Medicine, p. 519, Dec., 1973. From these attempts, to image non-linear parameters, a low frequency pumping wave is generated in a direction perpendicular to a signal ultrasonic wave or in a direction opposite thereto, so that a change in the phase of the signal ultrasonic wave is detected.
With this method for imaging the non-linear parameters of organ in accordance with a change in the phase of the signal ultrasonic wave, since the signal ultrasonic wave and the pumping wave are radiated in orthogonal directions or in opposite directions, it is very inconvenient for diagnosing human bodies. In addition, it is difficult to detect a change in the phase of the signal ultrasonic wave indicating a non-linear effect of the organ.